1. Field of Invention
The embodiment of the present invention relates generally to a converter and, more particularly, to a second-harmonic generation nonlinear frequency converter.
2. Description of Related Art
Recent years, demands for more convenient, robust and economical goods continue to rise with the advancement and progress of industry and social-economic. As such, products with more economic values are being developed to meet these and other needs.
In the mini-laser projection technology developed by CORININ and Microvision, the green laser is a wave-guide type and an x-cut PPMgLN with a length of 12 mm. In view of its technical indicator, a 10 ns, 1060 nm DBR-LD is used as a pump of the microminiaturization module to provide a narrow-band fundamental wave source (Δλ=0.16 nm) for second-harmonic conversion.
In this pump structure, the operation temperature of the PPMgLN is strictly limited to 25±1° C. so that three groups of temperature control devices are provided to keep the temperature of the 1060 nm laser source and the optical lens in a constant value. The consumption of the power source of the laser module and the stability of the system are the main concerns for the latter. The solution to the foregoing problem is to remove the limitation of the operation temperature and the temperature environment of the pump of the PPMgLN green light second-harmonic crystal.
One of the solutions is the limitation of the length of the crystal, PPMgLN having the quasi-phase-matching structure is adopted, and the product value of the green light conversion temperature-crystal length of the PPMgLN is T·L=2.1° C.-cm. The crystal length needs to be limited to 0.5 mm to make the PPMgLN crystal have a 40° C. operation temperature bandwidth.
However, the one-way transmission conversion efficiency of the second-harmonic crystal is low when operating with short length crystal. The problem of low conversion efficiency can be solved by using the optical cavity and adopting a 1064 nm infrared light source with short pulse in the optical cavity to increase the second-harmonic conversion efficiency. Additional optical components are needed in the foregoing solution such as a space holographic grating VBG to limit the 808 nm pump source bandwidth and increase the generation efficiency of the 1064 nm laser of the Nd:VYO4. Because the optical cavity is needed, the cost enhances relatively.
In view of the above, the existing apparatus still has obvious inconvenience and defects and needs further improvement. In order to solve the above problems, those skilled in the art are trying hard to find a solution, but no applicable method is put forward. Therefore, it is an important subject and also a purpose in need of improvement that how to improve the low bandwidth of the operation temperature of the nonlinear optical crystal and keep the conversion efficiency of the nonlinear optical crystal without increasing of the cost.